The contractor shall supply ERRB/NICHD investigators with (1) acute cell Leydig cell preparations, (2) specified amounts of rat or murine Leydig cells, and Nb2 Lymphoma cells cultured under experimental conditions defined by the Project Officer, (3) pseudopregnant rat ovaries (4) gonadal cell fractions (5) gonadal membranes and soluble receptor preparations. The contractor is also responsible for a) characterization of growth rates and metabolic functions during cell culture, histochemical analysis, assay cell surface receptors of steroid hormones and cyclic AMP produced under defined growth conditions, for maintenance and for the development of Leydig cells. b) for characterization and purification of cell fractions, and soluble receptor preparations and for development and characterization of antibodies to receptor preparations. Successful maintenance of Leydig cells in vitro will be evaluated in terms of growth rate and morphology, and retention of specific Leydig cell functions such as gonadotropin-binding and steroidogenesis. The cells are established in vitro, the contractor will maintain continuous cultures of Leydig cells.